1. Field of the Invention
The invention relates to an adjustable steering column for motor vehicles.
More particularly, the invention relates to a depth-adjustable (axial adjustment) or depth and height-adjustable (axial and radial adjustment) steering column, the steering column comprising a tubular body slidably mounted in a support assembly, means for adjusting the position of the tubular body in the support assembly and for locking in the desired position, as well as a device enabling to dissipate or absorb the energy generated during a frontal collision of the vehicle with an obstacle, following an impact of the driver on the steering column.
2. Prior Art
The implementation of energy-absorption devices on steering columns is known per se. By way of example, it is worth quoting the patent application GB 2 281 539. However, the device described in this document, shows the drawback of imposing the use of structurally distinct members in order to obtain a device which fulfills both the energy absorption function and the axial retention function.
In order to attempt to overcome this drawback, it has been proposed in the international application WO96/04162 to combine the means for adjusting the position of the steering column with the energy-absorption mechanism. Thus, it has been proposed a device enabling to axially adjust the steering column and conjointly dissipate the energy generated by the driver impact on the steering column.
To do this, the steering column comprises a tubular body slidably mounted in a fixed support member, the tubular body bearing first locking means for a releasable engagement with second locking means. The steering column further comprises a cam element intended to bring the first and second locking means to come into engagement with each other and thus, lock the tubular body with respect to the support member. The second locking means are connected to an energy-absorbing device comprising an elongated guide strip arranged around a shaft secured to the fixed support member around which the elongated guide strip may be pulled. The arrangement is such that, in normal use, the tubular body can be adjusted by sliding into the support member then locked in the required position by said first and second locking means. When the vehicle undergoes a frontal impact, the energy applied on the steering column drives the tubular body into the support member (retraction of the tubular body), bringing the first and second locking means, locked together, to pull the elongated member around the shaft such as to absorb the energy.
The steering column of WO96/04162 and the associated absorption and adjusting device nevertheless exhibit several drawbacks.
A major drawback is the number of pieces necessary for implementing the device combining the functions for adjusting the steering column and for energy dissipation, and more particularly essential for maintaining the locking means locked together, depending on whether the locking situation is a collision-free locking situation or a locking situation without collision. In fact, in the collision-free locking situation, a spring forming member and a cam element are provided, the latter acting on the spring forming member in order to keep the second locking means engaged on the first locking means. However, when a collision occurs, due to the fact of the retraction of the tubular body into the support member, the spring forming member is no longer in contact with the cam element. Keeping engaged the first and second locking means is then carried out by additional means acting on the spring forming member. The additional means consist in a platform provided within the support member.
Moreover, the arrangement of the different means requires a precise positioning as well as an adapted dimensioning of the spring forming member in order to prevent possible friction between the spring forming member and the platform. Such friction would in fact hinder the implementation of the energy-absorption mechanism.
Likewise, the device of WO96/04162 is such that the first and second locking means, the spring forming member and the cam element impose specific locations in order to enable the implementation of the locking means and the energy-absorption mechanism.
Finally, due to the fact that the shaft around which the elongated guide strip forming the energy-absorption device may be pulled is secured to the support member and that the locking means are carried by the tubular body during the retraction of the tubular body, the absorption of energy is not always ensured at the start of the tubular body retraction. In fact, this depends on the position of the tubular body in the support assembly during the impact and on the original positioning of the pieces with respect to each other.
It also has been known from the French patent application FR 2 881 707 an instantaneous energy absorption device intended to equip a steering column, the device comprising a fixed intermediary member connected to the support assembly of the column, a movable intermediary member connected to the tubular body of the column and at least one energy absorption member connecting the fixed member to the movable member. More particularly, the energy absorption member is anchored to an anchoring pin provided on the mobile intermediary member on the one hand and to a retaining pin provided on the fixed intermediary member on the other hand. The fixed intermediary member is fixed to the support assembly by means of a ratchet mechanism.
Due to the fact of the number of pieces necessary for mounting the member enabling the energy absorption between the support assembly and the tubular body of the steering column, the assembling of the previously described absorption device to a steering column proves to be somewhat difficult. It particularly requires distinct fixations for each of the members forming the energy absorption device.